The park is already too big. There is plenty of space for them to continue to develop and expand including the Thunderbolt plot, Rocky Hollow area and Troll's Village. There's over a decade of development space available to the park, by which time other attractions may start reaching end of life and start vacating their envelopes too.
As a comparison - Movie World - including the entire Rivals footprint, WOZ land, FN Maze buildings, Wild West, Stunt Driver, LTRR showstage (entirely), green lantern and everything in between, comes in at around 130,000SQM - and some of those areas aren't generally guest accessible - such as FN sheds, half of the LTRR stage, AOS Kitchens etc (not to mention WOZ isn't open yet, and Scoob is down long term).
Dreamworld, EXCLUDING WWW, BB Studios, Vintage cars and the part of Cyclone that goes into WWW, as well as the maintenance sheds at the back and the admin offices near the front, and it's STILL about 176,000SQM - all of which is pretty generally guest accessible.
Dreamworld doesn't need as much land as Dreamworld has.